During the practice of golf, the player hits the ball to move it, by propelling it with a golf club constituted by a shaft, which comprises a head at its lower end, while its upper end is equipped with a handle, commonly called a grip.
At present, the clubs used by golfers at the tee, or start of the hole, to drive the ball long distances, are called woods. In the beginning, the woods were built in their entirety from wood, such as persimmon or other similar varieties. These clubs are still prized by many players; but they are not very "forgiving," given the low density of the material used and its uniform distribution behind the hitting surface of the club head. To overcome this problem, the "wood-metal" club was produced. This club incorporates the shape of the wood, by the head is made in its entirety of steel. Given the high density of material used and the weight restrictions imposed, the wood-metal club generally comprises a hollow steel head, normally produced using the lost-waxcasting process.
One property common to all heads, whether they are made of wood, steel, or a composite material, is that they all have a hitting surface which is inclined in relation to the ground and which is both convex in horizontal sections forming what is called the "bulge," and in vertical sections forming what is called the "roll." The convex shape in horizontal cross-section of the hitting surface is designed to correct ball trajectories which, because of the rotation of the head resulting from impact, undergo lateral deviation to the right or left. However, the corrections brought about by the current shapes of the hitting surfaces are not produced under good conditions, and the trajectories are particularly inaccurate. It is observed, in particular, that the heads do not perform symmetrically when the ball is struck off-center, either toward the heel or the tip of the head. Because the shaft and the neck are positioned on the heel side, the head tends to pivot less during a stroke offset toward the heel than when the stroke is offset toward the tip (where the head pivots in the reverse direction, and from front to back). Because the rotational motions of the head, added to the meshing effect, are the source of the right and left deviations from a rectilinear path, these deviations must be rectified through the geometry of the hitting surface, whose traditionally-accepted symmetry is thus called into question.